Remove Dhall dependency and ReaderT; use dotenv; create encryption key on startup if it doesn't exist

examples/.env.example

@@ -0,0 +1,6 @@
+environment="production"
+applicationHost="localhost"
+applicationPort="3000"
+dbFile="data/Purr.sqlite"
+linkLength="24"
+adminEmail="admin@purr.example.com"

examples/config.dhall

@@ -1,16 +0,0 @@
--- /config.dhall
-{- 
-  Default Dhall Configuration for Purr.
-  You will need to change all instances of "REPLACEME" with the 
-  appropriate details. Additionally, you may want to change the
-  applicationPort from 3000.
--}
-
-{ environment     = "production"
-, applicationHost = "REPLACEME"
-, applicationPort = +3000
-, dbFile          = "data/Purr.sqlite"
-, dbKey           = "REPLACEME!!!!!"
-, linkLength      = +24
-, adminEmail      = "james@eversole.co"
-}